Because of its transparency, accessibility, simplicity and availability, the sea urchin embryo has been widely[unreadable] used to study cellular interactions that also occur in human development and disease. That is why the sea[unreadable] urchin embryo nas been designated a NiH model system and isthe rationale for its use in this study. Our[unreadable] long-term goal is to understand the molecular basis of one fuhctipnaliy important cellularInteraction, namely[unreadable] the attachment of the developing gut (archenteron) to the roof of the blastoeoel. Our working hypothesis,[unreadable] based on our published preliminary results, is that secondary mesehchyme cells at the tip of the arehenteron[unreadable] bind to cells of the blastoeoel roof via ligands containing mannose/glucose moieties associatirig with lectin-like[unreadable] receptors for these ligands. These specific aims will test this hypothesis: We will determine: (1) if[unreadable] microdissected components of thes cellular interaction bind together via mannose/gluoose moieties and their[unreadable] receptors; (2) if molecules that we isolated from living embryos, that block the cellular interaction in live[unreadable] embryos, can be purified and characterized; (3) if the active components of these molecules are specific[unreadable] sugars and receptors; (4) if the purified molecules block the cellular interaction in living embryos; (5) if the[unreadable] molecules are localized on the right cell types arid at the right developmental time; (6) if masking the[unreadable] molecules in live embryos blocks the cellular interaction; (7) if the findings are similar in two species of sea[unreadable] urchins. This study is innovative and novel because the system is totally accessible to probes in living[unreadable] embryos and allows microdissection to isolate and access the components of the cellular interaction for[unreadable] direct experimentation. Of importance in this revision is that we isolated molecules by anion-exchange HPLC[unreadable] that meet criteria for mediating the cell interaction. Two active HPLC fractions contain 1 (35 kD) and 2 (35 kD[unreadable] and 150 kD) bands on PAGE. Milligram quantities of the pufifi.ed molecules are easily Obtainable and will be[unreadable] sequeheed and compared with known proteins;frorri various genome databases.[unreadable] Relevance to Public Health. This study will identify molecular mechanisms that control a specific cellular[unreadable] interaction using the exquisitely accessible sea urchin erhbryo, a NIH designated model. These mechanisms[unreadable] will be of major importance in the elucidation of similar mechanisms that control human development and[unreadable] cancer spread, in human systems that are not very accessible to experimentation.